This invention relates to thermally-responsive indicating devices. More particularly, it relates to devices which indicate the attainment of predetermined temperatures.
Thermally-responsive indicating devices are especially useful in preparing foods, particularly meats and fowl. By providing means by which the device indicates the attainment of predetermined temperatures, such devices can signal the degree of "doneness" of the food.
Such devices are, of course, known as exemplified by the number of patents issued thereon. Thus, see, for example, U.S. Pat. Nos. 3,140,611; 3,280,629; 3,479,876; 3,548,780; 3,559,615; 3,626,897; 3,656,452; 3,682,120; 3,693,579; and 3,965,849. The devices described in these patents employ fusible latching means for normally securing the indicating means in a non-indicating position relative to the housing of the device. Typically, the latching means employed in these devices comprise metal alloys or waxes.
While devices employing such latching means have proven useful, they have certain drawbacks. For example, the metal alloys are high density materials. Thus, in addition to being expensive, relatively large quantities of alloy must be utilized in order to provide a given volume of latching means thereby adding to the expense of such means. Moreover, such alloys are typically prepared from toxic substances such as bismuth, lead, cadmium, tin, etc.
Waxes have been suggested as replacements for metal alloys. However, they have not proven entirely satisfactory. Typically, waxes fuse over a relatively wide temperature range (e.g., 5.degree. C. or more). Thus, they do not provide a quick response when a predetermined temperature has been attained. Moreover, some of such waxes can be extracted from the indicating device during preparation of the food.
The present invention overcomes these disadvantages. It provides a thermally-responsive indicating device which employs a locking means that comprises a class of nitrogen-containing organic materials. This locking means is substantially less dense and less expensive than a corresponding volume of the metal alloys. Thus, devices of the invention require significantly less of the locking means per unit volume and thereby afford substantial cost savings. Moreover, the toxic alloys are replaced with materials which are considered nontoxic and, in the most preferred case, exhibit essentially no acute oral toxicity. Furthermore, the organic locking means employed in the present invention typically fuse over a narrow temperature range (e.g., 3.degree. C. or less) and are generally resistant to extraction from the device by water and cooking fats and oils. Thus, devices of the present invention are safe and provide a quick and accurate response upon attainment of a predetermined temperature.